1. Technical Field
The present invention relates generally to drop-on-demand ink-jet printers, and more particularly to such printers capable of producing continuous tone prints from multi-bit data signals.
2. Background Art
True continuous tone images generally require 256 gray levels for of each primary color. Many processes are known for producing digital images using ink-jet printing. Most of these processes do not provide adequate gray level for good continuous tone images. Two very common methods of forming images using ink-jet printing are called *continuous ink flows and "drop-on demand".
In continuous ink flow systems, the amount of ink reaching a receiver medium from the nozzle is controlled to provide the desired density of each image pixel. In this process, it is very difficult to accurately meter the amount of ink from one nozzle; the relative motion between nozzle and media blurs the image; and media wetting and ink dripping results from quickly transferring large volumes of ink. It has been very difficult to obtain 256 gray levels from the continuous ink flow technique, and moreover these systems are very expensive.
In drop-on demand systems, ink is delivered one drop at a time, and printed gray level is conventionally controlled by regulating the number of drops leaving the nozzle to be delivered to the receiver media. It is believed that a 256 gray level system has not yet been successfully demonstrated. It is also believed that the problem, that of getting enough density resolution with each drop lies, in difficulty controlling the number of drops from each nozzle; the relative motion between media and the nozzle; and/or the frequency of drop formation.